1. Field of the Invention
The present invention relates to an intake apparatus for a V-type 8-cylinder internal combustion engine, and more specifically to an intake pipe structure of the intake apparatus, which is suitable for die casting.
2. Description of the Prior Art
In prior-art intake apparatus for V-type 8-cylinder internal combustion engines, a pair of collectors are disposed over both right and left banks of an engine body, respectively as disclosed in Japanese Published Unexamined (Kokai) Utility Appli. Nos. 61-53528 and 62-49626. In the former Patent disclosure (61-53528), 8 intake pipes are arranged alternately in such a way that right-bank cylinders are connected to a left collector over a left-bank, and left-bank cylinders are connected to a right collector over a right-bank, respectively. In the later patent disclosure (62-49626), 8 U-shaped intake pipes are arranged alternately in such a way that right-bank cylinders are connected to a right collector over a right-bank (on the same side), and left-bank cylinders are connected to a left collector over a left bank (on the same side), respectively.
On the other hand, in the V-type 8-cylinder internal combustion engines with a bank angle of 90 degrees, there exists a single plane type where crankpins of a crankshaft are arranged at 180-degree angular intervals on a single plane and a double plane type where crankpins are arranged at 90-degree angular intervals on two planes. In practice, however, two-plane type engines are widely adopted on the market.
In the above-mentioned two-plane V-type 8-cylinder engines, the order of cylinder ignitions are beginning from the engine front end as follows: "1 (1st cyl)-2 (2nd cyl) -7 (7th cyl)-3 (3rd cyl)-4 (4th cyl)-5 (5th cyl)-6 8". In the prior-art engine, however, since the cylinders are simply separated and connected to the right and/or left collectors disposed over the right and/or left banks, respectively, there exists a problem in that two cylinders into which intake air is introduced successively are connected to one of the two collectors, so that it is impossible to effectively introduced intake air into each cylinder, successively.
To overcome the above-mentioned problem, the applicant has already proposed an intake apparatus for V-shaped internal combustion engine, by which two cylinders into which intake air is introduced successively are perfectly divided into two collectors, as stated hereinbefore under RELATED APPLICATION.
The intake apparatus already proposed by the same applicant and the same inventor will be described in further detail hereinbelow. In FIG. 1, a first subcollector is arranged over a first bank (not shown) along which 1st, 3rd, 5th and 7th cylinders are arranged, and a second subcollector is arranged over a second bank (not shown) along which 2nd, 4th, 6th and 8th cylinders are arranged. The 1st and 7th cylinders on the first collector side are connected to the opposite second collector via 1st and 7th intake pipes P1 and P7; the 2nd and 8th cylinders on the second collector side are connected to the first opposite collector via 2nd and 8th intake pipes P2 and P8; the 3rd and 5th cylinders on the first collector side are connected to the first same collector via U-shaped 3rd and 5th intake pipes P3 and P5; and the 4th and 6th cylinders on the second collector side are connected to the second same collector via U-shaped 4th and 6th intake pipes P4 and P6. In the intake apparatus as shown in FIG. 1, however, since the 1st and 2nd intake pipes P1 and P2 arranged on the engine front side and the 7th and 8th intake pipes P7 and P8 arranged on the engine rear side all extend from one cylinder head on one bank side to a collector arranged over the other bank side obliquely in intersectional arrangement, and additionally the other four intermediate intake pipes P3, P4, P5 and P6 extend from one cylinder head on one bank side to a collector arranged over the same bank side into U-shape in butt arrangement, there exists a problem in that it is practically impossible to cast these intake pipes integral with the first and the second collectors.
To overcome the above-mentioned problem, it may be possible to cast the intake apparatus as shown in FIG. 1 by dividing the eight intake pipes into four groups of two intake pipes formed integral with the right and left collectors and right and left cylinder heads, respectively. In this method, however, it is impossible to equalize the two pipe lengths of the first and third pipes P1 and P3, for instance by joining the two pipes on the same flange plane. In other words, since a plurality of flanges must be formed at different locations, there exists another problem in that the manufacturing process is extremely complicated.
Further, it is also possible to consider to divide eight intake pipes into upper and lower portions by a single roughly horizontal plane between the two cylinder heads. In this case, however, since the obliquely extending intake pipes (e.g. P1, P2, P7, P8) are cut off at an inclination angle with respect to each central axis of each intake pipe into an oval shape, when the cut-off pipe ends are connected by two flanges. There exists a problem in that air flow resistance increases markedly due to stepped change in cross-sectional area, when the two flange portions are a little offset or misaligned from each other because of casting or assembly error.